Ahh yes W126 water leak's are fun to track down. You really need to just spray the car and poke around. It could be your door seal or even the window seal. The sunroof is easy to inspect, just make sure the drains are clear. If they are clear it won't leak. Their are two drains in the front corners of the sunroof, I usually shoot compressed air down them. I guess you could also shoot some water down them.

As for the trunk their are a couple common spots:
The antenne seal, if its hard just replace it. It costs $2 so don't mess with it.
The rear light seals also will leak and weep down into the wells, making it look like something else is leaking.

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1969 280SE
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